Field of the Invention
The present invention is in the field of data compression and storage. In particular, the invention provides a method and apparatus for coding and transforming video signals for compressed storage for use with personal video recorders in an interactive television environment.
Description of the Related Art
New forms of television communication include the possibility of interactive television wherein a broadcaster cannot only send its programs to the viewer, but the viewer can send information back to the broadcaster. Content from the broadcaster typically includes network programs and commercials, as well as web pages, interactive televised programs, graphics and text, and other items. At the same time, a viewer may communicate with a broadcaster or other entity (e.g., a third party website) via a television set-top box or similar device. Users/viewers may interact with the systems by ordering advertised products or services, requesting specialized information regarding particular programs, or navigating through pages of information.
At the center of this communications stream is a set-top box (STB) which receives the broadcast content. Generally speaking, the STB includes “middleware” and related software configured to control the flow of received broadcast programs, internet traffic, and data conveyed from the viewer. Also included in a viewer's STB (or coupled to the viewer's STB) may be the ability to record broadcast data for later use.
There are several methods currently in use by which viewers may record television broadcasts. One such method includes the use of a Video Cassette Recorder (VCR) which records received broadcasts onto video cassette tapes. Newer recording devices include Personal Video Recorders (PVR) which are typically coupled to a viewer's set-top box. PVRs typically include features that extend beyond the capabilities of conventional VCRs. One such feature is the ability to pause and rewind during the recording of a live broadcast. The recorded portion may then be viewed later or skipped to catch up to the real-time broadcast. Another possible use of the PVR is to record one television show while playing back another, previously recorded show. Typically, the PVR achieves these feats by recording compressed video signals on hard-disk drives so that they can be played back on command. However, PVRs have limited storage space (current typical values are about 40 Gigabytes). Moreover, a set top box (STB) which is configured to record may have even less storage when equipped with an integrated disk storage device.
One of the issues involved in recording programs concerns the quality of playback. Given a finite amount of recording space, there is a trade-off between the quantity of the signal one can record and its quality. To achieve higher quality, it is generally necessary to record more components of the signal being recorded and, in turn, use more space on the recording medium. Consequently, fewer high-quality images can be recorded on a medium than low-quality images.
In order to increase the amount of data which can be recorded onto a given medium, data compression techniques are frequently used. In the case of analog devices, varying levels of compression, and corresponding quality, may be chosen by a user. For example, VCR technology includes the possibility of recording at several levels of quality. VCR devices can currently be set to record at either lower or higher qualities. Creating a high quality recording generally requires more recording tape than does a low quality recording. Consequently, a viewer can record more programs at low quality settings that at high quality settings.
Other compression methods have been used with video file servers which may serve MPEGs requested by clients. Generally, the bit streams which are stored in these server libraries are typically coded at high quality levels and clients may request these video programs at different levels of video quality. However, the number of users and the quality of video delivered to the users is constrained by the outgoing channel capacity. To simultaneously accommodate the plurality of users who are demanding different levels of video quality, the video file server may scale the stored bit streams to a reduced bit rate. The video signals can then arrive as compressed data at the set-top box. In this instance, only the broadcaster needs to be equipped with the scaling hardware.
Newer television devices, including the set-top box and the PVR, have expanded the abilities of recording methods. New possibilities, such as playing back one recorded program while simultaneously recording another, are beyond the capabilities of the VCR. In order to support expanded abilities, the ability to record a greater amount of video within the STB storage or a digital PVR may be needed. There is also a desire for greater viewer control over the quality of the video stored in the viewer's PVR and to offer the consumer the opportunity for recording a greater number of hours with a smaller and less expensive storage device. Finally, in view of the above, there is a desire to make efficient use of the limited amount of disk space that is available in a PVR or similar device.